In total, there are 12 exposed screws to remove from the back plate. Those 4 near the hinge (green) are captured screws and will remain with the backplate. 2 shorter screws (purple) retain the optical drive and must be removed prior to the drive. The remaining 7 (black) are standard screws.

Note: Retain screws within a lidded or magnetitic container during replacement to prevent accidental loss.